Magic Mote thermostat and wireless temperature sensor


Tom’s another cool project theĀ Magic Mote thermostat and wireless temperature sensor:

A homemade thermostat up in the basement rafters controls the heating in my home. The smart bit is the radio frequency communication that connects it to a remote temperature sensor.

So, I’m planning a home automation system based around wireless nodes (the Magic Mote featuring a MSP430G2553 low power microcontroller plus NRF24L01+ 2.4 GHz radio module). Part of the motivation for doing this is that the wires between the furnace in the basement and the thermostat 2 floors up have broken and it’s a terrible nuisance to fish new wires in a 100 year old house with knob and tube wiring inside the walls.

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  1. Thanks for the info Tom :)
    Do these units have their own internal setup to re-transmit data that didn’t get through or are they ‘dumb’?

  2. I have only tried out some of the simplest modes of communication. For the sensor node that meant transmitting to the thermostat, and turning on the orange LED if the message was not acknowledged. Receiving the acknowledgement raises an interrupt in the IRQ pin and wakes the sensort, which is really a waste of battery power. But for a demo, and to locate where to get a good signal, it was worth doing. Once the system is properly up and running you’d probably want to disable that feature. For this specific purpose it didn’t seem to make sense to retransmit. The measurements are laggy anyway. Just read another data point and send that next time.

    1. One other thing, I meant to transmit time stamps along with the data so that the thermostat could always choose the most up to date measurements. But I forgot to include that feature, or rather the “Project of the Month” deadline came up too soon to implement it.

  3. Thanks again Tom, I was thinking of different applications where battery life wouldn’t be a huge issue. I know some of the Dorji models have modes where they basically take care of handshaking and CRC (or Checksums or whatever) to ensure the data gets through with (if physically possible) without the user having to do anything – essentially just throw the data at it and have reasonable confidence it will get through correctly and without errors (assuming single levels OK, etc.)

    I do a bit with serial (as in RS232) and these look like they could be handy for short range stuff – especially considering they are nice and cheap :)

    1. AFAIK the Nordic module handles CRC and acknowledgment in hardware. Certainly I want my sensor nodes to wake up, shout, and go back to sleep without worrying about all that. spirillis/nrf24/wiki on github has the low down, it is very informative. There is another library by “maniacbug” who has done development on an AVR platform. I don’t think either library supports mesh networking but for simpler topologies like trees I think everything is pretty straightforward.

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